This invention relates to a system that permits an operator to safely navigate a vessel in a water channel or harbor by using the Global Positioning System (GPS). The GPS is used to determine position (3-dimensionally) on earth by using a set of 24 geo-synchronous, earth-orbiting satellites broadcasting precisely timed signals. A GPS signal receiver (or GPS receiver) on earth is able to simultaneously read transmissions from at least four of these satellites to determine global latitude, longitude, time and elevation. The most widespread use, and the purpose of the GPS creation, is global navigation. Inexpensive GPS signal receivers are capable of providing one's location to within about 300 feet horizontally and 50 feet vertically. Greater accuracies are currently disabled or non-military receivers by the U.S. Department of Defense.
To obtain the water depth while on a ship, various types of Instruments and systems have been used to inform personnel of the water depth in channel and harbors. One common method is to rely on previously made measurements from the keel to the bathymetry (sea bottom topography). However, in doing so it must be recognized that the bathymetry changes with sediment transport from upland rainfall, runoff and shifting sand from long shore transport and coastal storms. As a result the previous measurements may not reflect the true conditions at the time the operator is in the channel.
Another prior art patented system discloses a signal processor which receives signals from an array of transponders to determine and record ranges to specific transponders, with the information received being recorded in a computer which transfers the information to a visual display.
With another prior art system used to measure ocean depths, acoustical sounding from a ship is used with pulses of different frequencies. The echoes are received at the ship and sorted by specific frequency. By doing so the user is assured that the determination of the transit time of a pulse of one frequency is not confused by the receipt of an echo at another frequency.
Still another prior art system discloses a system for locating a bottom cable which uses transponders connected to the cable and a master transponder which broadcasts an interrogation pulse from each transponder. Slave transponders send encoded signals to the master transponder and the time between the pulses is measured to constitute a range measurement to the slave transponder.